Data carriers (ID tags) which maintain data in non-contact identification systems continue to be miniaturized, and the current focus is on producing a smaller, cheaper data carrier which is suitable for a variety of applications. These might include access control systems which allow a person with a data carrier or ID tag to enter, uniform collection systems for hospitals or restaurants, and tracking systems to keep track of articles of clothing at cleaners or laundries. Data carriers which are to be attached to clothing for laundry identification must be waterproof and heat-resistant so that they will not be damaged during cleaning. Because they are used for such a variety of applications, it is essential that data carriers be mass-produced as cheaply as possible, in the fewest possible processes, and in the shortest possible time.
We shall now explain the existing methods of producing data carriers. A first method is shown in FIG. 7. Toroidal antenna coil 102 is placed in case 101. An electronic circuit unit (hereafter referred to as functional component 104) which contains a packaged IC is placed on printed circuit board 103 in case 101. The spaces are then filled with a resin 105, such as an epoxy resin or the like, to complete the data carrier.
A second method used to produce data carriers is transfer molding, which is illustrated in FIG. 8. Antenna coil 102 and functional component 104, which is connected to the antenna coil, are supported in a chamber inside molds 111 and 112. The chamber is filled via a narrow gateway with a thermosetting resin, such as epoxy resin, and the assembly is heated for several minutes to set the resin.
A third method used to produce data carriers is press molding. As shown in FIG. 9(a), a data carrier unit consisting of antenna coils 102 and functional component 104 is sandwiched between sheets 121 and 122 of vinyl chloride (PVC) and press-molded. Once pressed, as can be seen in FIG. 9(b), the work becomes a flat plate 123. Then, as is illustrated in FIG. 9(c), round plugs are punched out of the plate to produce two flat data carriers.
A fourth method uses injection molding to seal the data carrier. In this method, as is shown in FIGS. 10(a) and (b), a data carrier unit consisting of antenna coil 102 and functional component 104 is inserted into tray 131, which is produced by a molding process. Two of these assembled trays are then placed in the depressions in lower mold 132. Then, as is shown in FIG. 10(c), the lower mold is covered with upper mold 133, which also has two depressions in the locations which correspond to those in the lower mold. A thermoplastic resin is then injected at high pressure via the gates in upper mold 133 to form two button-shaped data carriers.
The above-described methods used in the prior art to produce data carriers are subject to the following problems regarding the water-resistance of the carriers and their ability to be mass-produced. With the resin-filling method shown in FIG. 7, the spaces must be filled slowly to prevent air bubbles from occurring. In addition to the care required in filling the spaces with resin, this method requires several hours for the resin to set.
The transfer-molding method shown in FIG. 8 entails pressure-molding for several minutes, and it requires that the resin be cured by maintaining it at a high temperature for several hours or longer. Also, the high pressure required to seal the functional component in resin makes it liable to slip out of position. FIG. 11(a) shows the correct placement of antenna coil 102 and functional component 104. When the spaces in the mold are filled with resin, these components have a tendency to slide out of the center of the data carrier. The displacement of the functional component within the molded unit is not the only problem with this method. As can be seen in FIG. 11(b), antenna coil 102 and functional component 104 may also protrude from the surface of the resin seal.
In the press-molding method shown in FIGS. 9(A)-(C), a punch process is required after the work is pressed to produce a round flat carrier. This extra process requires additional time and effort. And since only a vinyl chloride or another resin with low heat resistance can be used for the sheet material, this method cannot be used to produce heat-resistant data carriers.
The injection molding method produces a data carrier in a short time; however, just as in transfer molding, the high pressure required tends to force the functional component out of its proper position. And because it is injected under such high pressure, the resin may damage functional component 104 when it strikes it dead center, as shown in FIG. 12(a). For these reasons, manufacturers tend to inject the resin at a lower pressure, which results in a rougher-textured product that is easier to damage. Also, a parting compound is added to the resin so that the finished data carrier can be removed from the mold easily. Repeated incidences of heat shock may cause cracks to occur in surface 135 where seal 134 is in contact with tray 131. Since this may result in the seal separating from the tray, the injection method cannot guarantee a hermetic seal.
Although the injection mold has small air exhaust channels in it, if the components in it have a more complex shape, air pockets may form between the functional component and tray 131, as shown by the dotted lines in FIG. 12(b). If the work is molded at high temperature with these air pockets in it, the air will push tray 131 away from the functional component, and it will not be possible to achieve the specifications for which the mold was designed.
As can be seen in FIG. 13(a), the lead cable 102a of antenna coil 102 is normally passed under the body of the coil and connected to the functional component during injection so that it will not be damaged. Nevertheless, the injection pressure applied to antenna coil 102 may damage the insulation on the lead cable 102a. If this happens, the inductance and the resonant frequency will deviate from their specified values and the data carrier will not maintain its characteristics.